Preparation of modified soy protein



Patented Apr. 4, 1950 1 PREPARATION OF MODIFIED SOY PROTEIN Louis Salt and menu-a Rathman, Decatur, Ind., assignors to Central Soya Company, Inc., Fort Wayne, lnd., a corporation of Indiana .No Drawing.

This invention relates to the preparation of modified soy protein, and more particularly to modified glycinin which is particularly adapted for use as a whipping agent for the preparation of nougats, fudge, divinity and cream candies, meringue powders, and for a large number of other food uses.

An object of the invention is to prepare a modified soy protein which has superior whipping stock will consist of soy bean'meal to which the process of the invention is applied. However, the invention is also applicable to soy protein in less or more pure form.

In accordance with the invention, the glycinin of the soy protein, which as isolated from the Application September 4,1945, Serial No. 614,442

5 Claims. (0]. 9914) glycinin is also hydrolyzed and is found in the product to contain nitrogen in the non-protein form.

In treating soy bean meal, the desired soy protein is separated from the other constituents of themeal. The first step may consist of extraction of the meal, which may be in the form of oil-free flakes, with water or with a dilute-alkaline solution at a pH substantially different from the qualities and which results in a foam of unusually isoelectric point of the glycinin. The isoelectric high stability. A further object is to provide range of the glycinin is in the neighborhood of 'modified soy protein which is miscible in water a pH of 4.2-4.6, and the extraction liquor should and will whip in this mixture to a fairly light have a pH at least as high as 6. A pH above 8 foam. A further object is to provide a process of should be avoided in order to avoid discoloration controlled modification for the soy protein which -3 of the soy protein and deterioration. of the whipresults in a product that may be whipped with ping propertiesv of the modified protein which water, corn syrup, and cane sugar to yield a is later produced.

frapp of good body, unusually high stability, Although water may be used for the extraction, desirable shortness, and substantial freedom from an alkaline material, such as sodium sulfite, soany tendency for the separation of a liquid layer dium carbonate or sodium hydroxide, is'preferover at least a one-month storage period. ably added to the water in a quantity sufficient In general, the treatmentof the soy protein to bring the pH of the extracting liquor to the may be in a series of steps in which the glycinin desired range. Preferably, .this pH is in the is isolated from the other soy bean constituents neighborhood of 6.4-6.8. Sodium sulfite is parand subjected to controlled modification. ,The ticularly suitable for this purpose since it serves steps may consist of the extraction of the protein not only as an alkaline buffer, but also acts as an .in soluble form from soy bean meal, the preantiseptic and produces better quality protein cipitation of the glycinin from the water-soluble product. extract at or near the isoelectric pH range of The extraction of the soy bean meal with the the glycinin, the washing of the precipitated 3o dilute alkaline solution may be carriedout at a glycinin, the enzymatic modification of the slightly elevated temperature, preferably in the glycinin, and the termination of enzymatic modineighborhood of 130 F. The solution is filtered fication by the adjustment of the pH. to separate the insoluble materials, diatomaceous In our earlier operations, the enzymatic modiearth preferably being used as a filter aid. Infication of the glycinin was halted at the desired stead of filtration, any suitable means of seppoint by heat treatment which was a useful step arating the soluble constituents and insoluble and which present. certain additional "adconstituents, such, for example, as screening or vantages in the process. We have discovered that centrifugation, may be used. The soluble conwhen the heat treatment is omitted and instead stituents consist of the bulk ofthe protein, the a control of the enzymatic modification accom- 40 soluble carbohydrates, and thesoluble inorganic plished solely by the adjustment of the pH, the I salts. The insoluble constituents consist of the frapp produced through the use of the product ,fiber, any residual oil which is present, a portion has considerably greater stability. of theprotein, and a portion of the carbohy- The invention is applicable to soy protein in drates. I any suitable form. Ordinarily, thesoy protein The extraction liquor containing the soluble constituents is subjected to the secondstep of the process, which consists of the precipitation of the glycinin at the isoelectric pH range thereof.

This is accomplished by acidifying the solution to adjust the pH to a range in the neighborhood of 4.2-4.6. Sulfur dioxide, hydrochloric acid, or

' any suitable acidifying medium may be used for adjusting the pH. When the pH'is adjusted to in' the form of curd solids. Any soluble constitu-a outs, including the soluble inorganic salts and 'of water-soluble protein is obtained in the product through the use of this enzyme. The modification is carried out under conditions of temperature and pH which are favorable to the activity of the enzyme. In the case of pepsin, a pH in the neighborhood 'of 2 to 3 and a temperature of 100 F.-110 F. is to be preferred. We have found that especially good results are obtained where we use 0.5% pepsin and employ a pH of 2. Adjustment of the pH may be made by the addition of any suitable acidifying agent, such as sulfuric or hydrochloric acids. However, phosphoric acid has been found to be particularly suitable for this purpose.

The enzymatic modification is carried out by treating the glycinin curd in water whereinthe solids content of the solution is in the neighborhood of 11% to 13% by weight, within the neighborhood of 0.5% by weight of commercial 1:10,000 potency pepsin at a pH of 2 and a temperature of 100 F.

Modification is continued until the desired percentage of the glycinin is soluble in water at a pH of 5.0. We prefer to continue it until 40% of the glycinin is converted to soluble protein. The product may also contain at least 20% but preferably not more than 35% of the total nitrogen present'in the non-protein form. It is important that the modification be limited because if too extensive modification or hydrolysis occurs, the modified protein will not have the desired whipping properties. On the other hand, if the modification is insufficient or too limited, the protein also lacks the desired whipping properties and. solubility.

Preferably, the modification is continued until the water solubility of the nitrogenous materials in the product is between 50% and 70% at a pH of 5. It is also preferred that the non-protein nitrogen content of the product be in the range of 25% to 35%. Of course, the extent of modification may be varied according to the type of product which it is desired to obtain. When the modified protein is to be used in the form of a frapp, such as for nougats, the modification may be carried on to a point where in the neighborhood of 60% of the nitrogenous material in the modified product is water-soluble at a pH of 5. This product issubstantially miscible inwith this procedure, one gram of the product is dispersed in 50 ml. of water and the pH of the suspension is then adjusted to 5. The suspension is then mechanically shaken for 30 minutes and the volume brought to 100 ml. in a volumetric flask. The suspension is centrifuged for 30 minutes at a temperature of 22 C.-26 C. at 2,000 R. P. M. (centrifuge radius 7.5 inches) The product remaining in the supernatant liquid is considered the water-soluble product while that which is removed in the centrifuging is considered as water-insoluble. The term water-soluble as used herein is intended to refer to a product which remains in the supernatant liquid unde these conditions.

The term protein or modified protein as used herein refers to a product which is precipitated by trichloroacetic acid under the following conditions: A one gram sample or the product is weighed into a 200 ml. centrifuge bottle and extracted with 40 ml. of 0.8N. (13.6%) trichloroacetic acid for one-half hour in a mechanical shaker. minutes at 2,000 R. P. M. (centrifuge radius 7.5 inches). The supernatant liquid contains the non-proteinfraction, while that portion of the product which is separated by the centrifuge is referred to as protein. This method of determination when applied to non-protein nitrogen is described by H. C. Becker, R. T. Milner, and R. H. Nagel, Cereal Chemistry 1'1, 447-457 (1940).

Water-soluble protein as referred to herein is that which is precipitated and separated by the .Becker trichloroacetic acid test, but which remains in the supernatantliquid under the Smith centrifuging test at a pH of 5.0. Water-soluble nitrogen is determined by the Kjeldahl-Gunning- Arnold method on the product remaining in the supernatant liquid after the Smith centrifuge separation. Non-protein nitrogen is determined by the Kjeldahl-Gunmng-Arnold method on the supernatant liquid remaining after the Becker trichloroacetic acid test.

When the protein has been modified to the desired extent and it becomes important to halt further enzymatic activity, we adjust the pH to 6.5 with 10% sodium hydroxide; No heat is employed to inhibit enzymatic activity and a complete control is accomplished through the abovementioned change in pH. The resulting product when formed'into a frapp, as described, has an unusually high stability and thus surpasses the product formed by the employment of heat for halting enzymatic modification.

While in'the foregoing description, we have set forth certain specific steps and materials as illustrative of 'one successful process embodying the invention, it will be understood that such steps may be widely modified and equivalent materialsemployed without departing from the spirit of our invention.

We claim:

1. In a process for preparing modified soy protein, the steps of subjecting glycinin to enzymatic modification with pepsin under conditions of hydrogen .ion concentration and temperature which are favorable to the action of the enzyme until at least 60% of the product is soluble in water at a pH of 5.0 and until the non-protein nitrogen content is between 20 and 35%, and then raising the pH to halt further enzymatic modification.

2. In a process for preparing modified soy protein, the steps of subjecting glycinin to enzymatic modification with pepsin under conditions of hydrogen ion concentration and temperature which are favorable to the action of the enzyme until about 70% of the product is soluble in water at a pH of 5.0 and the non-protein nitro- The suspension is centrifuged for 15 gen is less than 35%, and then raising the pH to halt further enzymatic modification.

3. In a process for preparing modified soy protein, the steps of subjecting glycinin to enzymatic modification with pepsin under conditions of hydrogen ion concentration and temperature which are favorable to the action of the enzyme until about 70% of the product is soluble in water at a pH of 5.0 and until the non-protein nitrogen content is between 20 and 35%, and then raising the pH to halt further enzymatic modification.

4. In a process for preparing modified soy protein, the steps of subjecting glycinin to enzymatic modification with pepsin under conditions of hydrogen ion concentration and temperature which are favorable to the action of the enzyme. the percentage of the pepsin being 0.5% based on the glycinin, until at least 60% of the product is soluble in water at a pH of 5.0 and until the non-protein nitrogen content is between 20 and 35%, and then raising the pH to halt further enzymatic modification.

5. A process for the preparation of a soy protein whipping agent, comprising extracting with REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Date Number 4 Name 1,754,825 Heuser Apr. 15, 1930 2,217,264 Weizmann Oct. 8, 1940 2,381,407 Levinson et a1. Aug. 7, 1945 

1. IN A PROCESS FOR PREPARING MODIFIED SOY PROTEIN, THE STEPS OF SUBJECTING GLYCININ TO ENZYMATIC MODIFICATION WITH PEPSIN UNDER CONDITIONS OF HYDROGEN ION CONCENTRATION AND TEMPERATURE WHICH ARE FAVORABLE TO THE ACTION OF THE ENZYME UNTIL AT LEAST 60% OF THE PRODUCT IS SOLUBLE IN WATER AT A PH OF 5.0 AND UNTIL THE NON-PROTEIN NITROGEN CONTENT IS BETWEEN 20 AND 35%, AND THEN RAISING THE PH TO HALT FURTHER ENZYMATIC MODIFICATION. 